1. Field of the Invention
This invention relates generally to a friction control element, such as a clutch or brake for an automatic transmission, and, more particularly, to establishing a stroked position for the control element.
2. Description of the Prior Art
In an automatic transmission for a motor vehicle step changes among forward gears occur when one or more friction control elements engage or disengage. In an automotive transmission it is conventional to use hydraulically actuated friction control elements that include interleaved discs and plates, which become frictionally engaged mutually when a drive connection is to be closed and disengage when the connection is opened.
A clutch or brake is stroked when its torque transmitting capacity is about zero and most of the clearances between components are absent, but the control element is ready to increase its torque capacity promptly with little additional displacement.
One factor in causing a noticeable bump during a synchronous shift from second gear to first gear shift in a transmission is the inability to determine reliably the stroke position of a clutch that causes no tie-up bump. If the friction control element is not stroked, engine speed flares.
Conical friction clutch and brakes have been developed, which employ rings having conical serrations that alternately engage and disengage to open and close a drive connection between members, to which the rings are secured. These conical clutches and brakes, however, provide no stroked state or a means for determining the degree of displacement that places the control element in a stroked position or state.
A need exists in the industry for a technique that allows reliable stroking and holding of a conical friction control element in a stroked position before its mechanical or frictional engagement.